In many applications of microfluidics it is desirable to create a concentration gradient transverse to the flow in a channel. The gradient may be used to efficiently optimize reactions and to eliminate the need for preparing a large number of individual dilutions. Examples of such uses are found in microfluidic systems for drug discovery, material science, and use with tissue cultures. A chemical gradient is also useful in separation methods, such as in isoelectric focusing, where molecules separate into zones each having a specific pH.
Because laminar flow typically prevails in microfluidic systems, mixing is difficult to achieve. Therefore special techniques are needed to achieve mixtures of two input fluids. A number of gradient generators in microfluidic formats are known in the art. These typically involve complicated networks and microstructures designed to divide and mix streams in laminar flow, thereby converting two input concentrations into an output stream with a transverse concentration gradient. These devices generally require intricate micromachining and comparatively long lengths on the order of several centimeters. These devices are, therefore, typically expensive to manufacture and limited to applications where long channel lengths are acceptable.
As a result, there is a need for a flow gradient-generation device that may be used to create transverse concentration gradients of differing fluids in laminar flow channels of limited channel length.